This is an electrophysiological and anatomical investigation of the activity dependence of synapse elimination both during regeneration (as a model for development) and in the mature retinotectal projection of goldfish. It seeks to understand the role of activity in setting up and maintaining precise orderly connections, and takes advantage of four features of this system: 1) the ease of surgical manipulation in adult fish, 2) the ability of the optic fibers to regenerate a precise retinotopic projection, 3) the geometry of the eye which allows the containment of tetrodotoxin for long term block of activity and 4) the known nicotinic cholinergic pharmacology of retinotectal transmission in fish and frogs which allows blocking of synaptic transmission. The working hypothesis is that correlated activity, a property of near neighbors in the retina, is used as a cue to concentrate the initial diffusely regenerated arbors into correct areas in the overall map. This will be tested by 1) blocking all activity with TTX, 2) synchronizing all activity with strobe light or 3) blocking all transmission with continuous AlphaBungarotoxin application to the tectum during regeneration; and assessing targeting of arbors via electrophysiological mapping and single fiber HRP fills in whole mounts. Local blocking experiments with AlphaBungarotoxin show that arbors move out of blocked regions to make effective synapses elsewhere. This will be further investigated with the single fiber whole mount technique and also quantitatively at the electron microscopic level. There are two health related aspects. First the phenomenon of activity dependent synaptic stabilization and competition in neural development is germane to developmental disorders such as amblyopia. Secondly the failure of axonal regeneration in mammalian central nervous system makes most neurological damage irreversible. Better understanding of successful regeneration in lower vertebrates may lead to strategies for therapeutic restoration of this ability in humans.